The mass-size plane of EAGLE galaxies

Abstract

Current observational results show that both late-and-early-type galaxies follow tight mass-size planes, on which physical properties such as age, velocity dispersion and metallicities correlate with the scatter on the plane. We study the mass-size plane of galaxies in cosmological hydrodynamical simulations, as a function of velocity dispersion, age, chemical abundances, ellipticity and spin parameters with the aim at assessing to what extent the current cosmological paradigm can reproduce these observations and provide a physical interpretation of them. We select a sample of well-resolved galaxies from the (100 Mpc)^3 simulation of the EAGLE Project. This sample is composed by 508 spheroid-dominated galaxies and 1213 disc-dominated galaxies. The distributions of velocity dispersion, age, metallicity indicators and gradients and spin parameters across the mass-size plane are analysed. Furthermore, we study the relation between shape and kinematic parameters. The results are compared with observations. The mass-weighted ages of the EAGLE galaxies are found to vary along lines of constant velocity dispersion on the mass-size plane, except for galaxies with velocity dispersion larger than aprox 150 km s^(-1) . Negative age gradients tend to be found in extended disc galaxies in agreement with observations. However, the age distributions of early-type galaxies show a larger fraction with inverted radial profiles. The distribution of metallicity gradients does not show any clear dependence on this plane. Galaxies with similar spin parameters ({\\lambda}) display larger sizes as their dynamical masses increase. Stellar-weighted ages are found to be good proxies for {\\lambda} in galaxies with low ellipticity ({\\epsilon}). Abridged